만성간질환에서항섬유화치료의과거와미래 가톨릭대학교성가병원소화기내과 이영석 Antifibrotic Therapy in Chronic Liver Disease: Past and Future Prospectives Young-Sok Lee, MD Department of Internal Medicine, Holy Family Hospital, The Catholic University School of Medicine, Korea Abstract Hepatic fibrosis is characterized by the excessive accumulation of multiple matrix components in the liver including the interstitial collagens, basement membrane collagens, proteoglycans, and matrix glycoproteins. Activated hepatic stellate cells, portal fibroblasts, and myofibroblasts are the major source of extracellular matrix in response to fibrogenic cytokines such as TGF- β. The fibrogenic process is dynamic and liver fibrosis is the net result of the imbalance between the collagen fiber synthesis and decomposition. The progress in understanding fibrogenic mechanism provided the development of effective therapies to reverse hepatic fibrosis and even cirrhosis. Removing the injurious stimuli, suppressing hepatic inflammation, down-regulating stellate cell activation and promoting matrix degradation are the mainstay of antifibrotic therapy. Many potential antifibrotic strategies based on apoptosis of the activated stellate cells, drug targeting to the fibrogenic liver cells, and combination therapy of multiple drugs in small doses are emerging but testing of their clinical efficacy and safety remains to be clarified. Key Words: Antifibrotic therapy, Stellate cell, Cirrhosis, Chronic hepatitis - 41 -
2006년대한간학회 Single Topic Symposium 서 론 간섬유화 (Liver fibrogenesis) 현상은간조직에서나타나는상처치유 (wound-healing) 과정의일 종으로서거듭되는간조직의손상과재생과정을통하여간경변증 (liver cirrhosis) 이발생되고있 다. 1 염증반응이진행됨에따라활성화된간성상세포 (hepatic stellate cell, HSC) 에서다량의교원 질을분비하고, 이는세포외기질 (extracellular matrix, ECM) 과결합(cross-linking) 함으로써간섬유 화현상은진행되고있다. 2 간조직내에교원질(collagen) 이다량침착되고, 재생결절 (regenerating nodule) 이교원질로이루어진다발(fibrous band) 로둘러싸여, 간조직의해부학적구조가비정상적 인상태(abnormal architecture) 로변한상태를간경변증이라하며인체내에서다양한종류의특 성을나타내고있다( 표 1). 효과적인치료방법이없었던지난날간손상의원인인자를제거하거나 염증반응을완화시킴으로서섬유의생성과정 (fibrogenesis) 을억제하는치료방법이항섬유화치료 의근간을이루어왔다. 섬유화현상이섬유의생성(fibrogenesis) 과용해(fibrinolysis) 사이에서의 동적인과정(dynamic process) 으로알려진상태 2 에서도간경변증자체가불가역적이라는인식이 지배적으로각인되어항섬유화치료는답보상태에있다. 만성 B 형간염, C형간염을포함한만성간 질환의치료방법이개선됨에따라간경변증의섬유화정도가호전된다는연구결과를토대로간경 변증자체도가역적질병이라는인식이보편화되고있다. 그러나간섬유화과정에관여하는유전적 요인이나환경적요인이무엇인지는아직까지문제점으로남아있다. 어느정도의간경변증까지항 섬유화치료를통하여가역적으로호전시킬수있는지도문제점으로남아있다. 간섬유화과정에 대한관심집중과광범위한연구를통하여항섬유화치료의효과를향상시킬수있을것으로기대하 고있다. Table 1. Characteristics of Liver Cirrhosis Biological Morphological Hemodynamic Physical Functional Increased role of activated HSC due to repeated necroinflamation Altered lobular architecture with regenerating nodules Impaired sinusoidal blood flow and portal hypertension Hardening nodular surface and shrinkage of the liver Impaired liver function and diminished hepatic reserve 간섬유증 간조직에서발견되는세포외기질에는 a) 교원질, b) 당단백질(glycoprotein), c) proteoglycan, d) glycosaminoglycan 이있으며각각의구성성분은표 2 와같다. 3 교원질은 glycine-proline- - 42 -
이영석 : 만성간질환에서항섬유화치료의과거와미래 hydroxyproline 을지닌단백질로서제1형부터제19형까지여러종류가있으나제1 형, 제3 형, 제4 형, 제5형및제6 형교원질이간과관련되어있는것으로알려져있다. 원섬유를형성하는교원질 (fibril-forming collagen) 은제1 형, 제3 형, 제5 형, 제6 형교원질이며, 제4형은 sheet를형성하는교 원질(sheet-forming collagen) 로서주로기저막(basement membrane) 을구성하고있다. 4 교원질은 주로활성화된간성상세포에서생성되며교원질의증가는간섬유화의중요원인이되고있다. 간 경변증환자의간조직내에서는교원질총량이정상때보다약 10 배이상증가되어있다. 5,6 간조직 내에서발견되는당단백은 fibronectin, laminin, thrombospondin, tenascin, undulin, entactin 등 이있으며이들은대부분 loose connective tissue, 기저막에존재하고있다. 2,6 정상간조직에서는 heparan sulfate (65.5%) 가가장풍부하고, dermatan sulfate (14.3%) 가다음을차지하고있다. 간 경변증때에는 heparan sulfate 가 2배증가하는데비하여 dermatan sulfate, chondroitin-6-sulfate 는약 10 배씩증가하고있다. 7 Table 2. Extracellular Matrix (ECM) Molecules in the Liver Collagens Glycoproteins Proteoglycans Glycosaminoglycan Type I Undulin Heparan sulfate Hyaluronic acid Type III Fibronectin Dermatan sulfate Type IV Laminin Chondroitin sulfate Type V Entactin Perlecan Type VI Tenascin Aggrecan Thrombospondin Decorin/biglycan Nidogen Syndecan/fibroglycan 간에서섬유생성 (hepatic fibrogenesis) 정상간에서는간세포, 동모양혈관내피세포 (endothelial cell) 및간성상세포에서세포외기질 (ECM) 이생성되지만, 간손상을받은후에는주로활성화된간성상세포에서세포외기질이생성되 고있다( 그림 1). 손상받은간세포나쿠퍼세포등에서분비된각종싸이토카인이나 oxidative stress 등에의해간성상세포가활성화되고있다. 활성화된간성상세포는각종성장인자에대한반응이증 가하고, 근섬유모세포 (myofibroblast) 유사형태의세포로변화하여다량의교원질을합성하고있다 ( 그림 2, 3, 4). 제1 형교원질은간성상세포를더욱활성화시키고있다. 여러가지싸이토카인중 TGF- β, PDGF 등이간성상세포활성화의가장중요한인자로작용하고있다. 8,9,10-43 -
2006년대한간학회 Single Topic Symposium Figure 1. Matrix and cellular alterations in hepatic fibrosis. Figure 2. Initiation, progression and maintenance of hepatic fibrosis. - 44 -
이영석 : 만성간질환에서항섬유화치료의과거와미래 QUIESCENT HSC FIBROGENESIS Portal fibroblast T mφ INITIATION & PROGRESSION & MAINTENANCE Growth factors Cytokines Chemokines Vasoactive factors Free radicals ACTIVATED HSC Figure 3. Changes of hepatic stellate cells after transdifferentiation. Hepatic stellate cell Transformation Myofibroblast Volume density of lipid droplet (<20%) Retinoid concentration Rough ER ECM gene expression Desmin, gelsolin,, SMA Glial fibrillary acidic protein Fibroblast-like like shape Modulation of cell surface receptors (cytokine receptors, integrins,, CAM) Figure 4. Functional changes associated with hepatic stellate cell activation and their stimuli. - 45 -
2006년대한간학회 Single Topic Symposium 세포외기질의분해 (matrix degradation) 인체내에서세포외기질이과량생성되면곧바로세포외기질의단백질분해효소에의한분해과정 (fibrolysis) 으로이어지고있다. Matrix matalloproteinase (MMPs) 가중요한단백질분해효소로작 용하고있으며인체의간에서는 MMP-1, -2, -3, -8, -9, -12, -13, -14 의여러종류가생성되고있 다. 11 MMP-2 는주로기저막을형성하고있는교원질과변성된교원질을분해하고, MMP-8 은원 섬유(fibril) 를형성하는교원질중주로제1형과제3 형의교원질을분해하고있다. 12 조직내에는 MMP 의활성을억제하는물질(tissue inhibitors of MMPs, TIMP) 이존재하고있으며, 4가지종류 의 TIMP 중 TIMP-1 이가장광범위하게작용하며또한가장중요한역할을담당하고있다. 항섬유화치료 섬유화과정(fibrogenesis) 은 1) 세포외기질의과량합성, 2) MMP 분해효소의합성과활성도의 저하, 3) TIMPs 합성의증가로특징지어지며그결과로나타난것이섬유화현상이다. 항섬유화치 료는크게 1) 간세포손상의원인자체를제거하는치료 2) 간조직내에서염증반응을완화시키는 치료, 3) 간성상세포를활성화시키고있는각종섬유화인자를억제시키는방법, 4) 활성화된간성 상세포의활성도를저하시키는방법, 5) 과량합성된세포외기질을분해하는방법으로구분할수가 있다. 2,13 일반적으로항섬유화싸이토카인의투여와섬유화싸이토카인의억제제를투여함으로써 세포외기질의합성을억제시키고있다. 또한활성화된간성상세포가 apoptosis 과정을통하여사 멸할수있도록유도하는치료방법도이용되고있다. 14,15 한편으로는간경변조직에서세포외기질 을직접적으로분해하기위하여간조직내에 MMP-1이나 MMP-8 유전자를주입하는치료방법 (adenoviral gene transfer) 도시도되고있다. 항섬유화치료는 1) 간조직에특이적으로작용해야 하며, 2) 오랜기간동안환자의순응도를유지할수있도록투여방법이간편해야하며, 3) 효과가 뚜렷해야하며, 4) 부작용이없어야하는조건을지니고있다. 특히잔여간기능이부족한간경변증 환자에게오랫동안투여하여도부작용이없고, 효과는뚜렷하며, 경제적으로부담이되지않는약 제의개발이요구되고있다. 간에서염증반응을완화시키는약제 간조직에서염증반응을완화시킴으로써간섬유화를억제하는약제로서는간기능개선제, 소염제, anti-oxidant 가있다. 일반적으로 UDCA, 실리마린, DDB 등이이용되고있으며, 알코올간질환에서 는 s-adenosyl methionine (SAM), propylthiouracil (PTU), polyenylphosphatiykcholine (PPC), - 46 -
이영석 : 만성간질환에서항섬유화치료의과거와미래 malotilate, anti-tnf-α 가사용되고있으며, 만성 C형간염에서는 IL-10, 비타민 E가이용되고있 다. 주성분이 silybinin인실리마린은간세포에서 RNA 합성을촉진시키고, 지질의과산화반응 (lipid peroxidation) 을감소시키며간성상세포의증식과콜라젠합성을억제시키는것으로알려져있다. 2 UDCA와 PPC 는간세포막을보호함으로써염증반응을완화시키고있으며, malotilate 는 cytochrome P450 2E1 을억제함으로써, SAM은 antioxidant인 glutathion을합성함으로써염증반응을완화 시키는것으로알려져있다. 15,16 자가면역성간질환이나알코올간질환에서는 corticosteroid 가이 용되고있으며, colchicine, 인터페론- 감마, PPAR ligand 가항섬유화약제로이용되고있다( 그림 5, 6). QUIESCENT HSC FIBROGENESIS T mφ Anti-inflammatory inflammatory Corticosteroid, IL-1 receptor antagonist TNF-α antagonist, IL-10 Portal fibroblast Growth factors Cytokines Chemokines Vasoactive factors Free radicals ACTIVATED HSC Antioxidants Sylimarin,, UDCA, DDB, Malotilate, Baikalein, Resvertol, Quercetin, TJ-135, NAc, SAMe, Figure 5. Roles of antiinflammatory drugs and antioxidants on activated stellate cells. - 47 -
2006년대한간학회 Single Topic Symposium QUIESCENT HSC T mφ FIBROGENESIS LIVER FAILURE Portal fibroblast FIBROTIC LIVER PROGRESSION & MAINTENANCE ACTIVATED HSC Recruitment of Inflammatory cells Collagen synthesis MMP-1/3/13 TIMP-1 TIMP-2 Collagen accumulation Figure 6. Effector role of activated stellate cells. 항TGF-β 약제들 섬유화촉진인자중가장강력한싸이토카인으로알려진 TGF-β 와관련하여항섬유화효과를 나타내는약제또는인자로서 decorin, camostat mesylate, soluble receptor, antibody, antisense nucleotide, naringenin, safironil, halofuginone 등이있으며각각의작용부위는그림 7-9에서와같 다. 17-20 - 48 -
이영석 : 만성간질환에서항섬유화치료의과거와미래 Latent TGF-β1 Interferon PPAR antagonist Angiotensin inhibitor Pentoxifilline Fibrosis Protease (upa upa) TGF-β1 Oxidative stress H 2 O 2 C/EBPβ Procollagen I Camostat mesylate Decorin Soluble receptor Antibody Antisense Sylimarin DDB UDCA Antioxidants Malotilate Baikalein Resvertol Quercetin TJ-135 (Vitamin E) NAc SAMe Figure 7. Oxidative stress and generation of hydrogen peroxide activate the TGF-β pathway. Smad-signalling Toll-like like receptor β-cathepsin III TGF-β II II/I Smad 2/3 TGF-β specific P Smad7 Inhibitory Smad P P Tf Co-activator Co-repressor Target gene Nucleus... Smad 4 Co-Smad Cytoplasm Figure 8. TGF- β signalling pathway. - 49 -
2006년대한간학회 Single Topic Symposium Oltipraz III TGF-β II II/I IFNγ Smad7 Inhibitory Smad Smad 2/3 TGF-β specific P P Naringerin P Tf Co-activator Co-repressor Ski SnoN Target gene Nucleus... Smad 4 Co-Smad Safironil Halofuginone Cytoplasm Figure 9. Antifibrotic drugs that principally inhibit TGF- β pathway. 활성화된수용체를목표(target) 로하는항섬유화약제의운반(delivery) 과치료 활성화된간성상세포의세포막에는콜라젠 VI 수용체(CVIR), PDGF-βR, endothelin A수용 체 (ET A R) 가항진(upregulation) 되어있다. 간성상세포는이미항진되어있는수용체를통하여 autocrine 또는 paracrine 방법으로 TGF-β 와같은싸이토카인의섬유생성자극을받아활성화상 태를계속유지하고있다. 이들수용체의 antagonist 를이용하여, 또는 peptide analogue 를이용하 여, 수용체를직접적으로차단시키면섬유화현상은진행되지않고있어항섬유화치료의목표 (target) 로이용되고있다. 4 이들수용체와반응하는 ligand를항섬유화약제에결합시켜놓으면항 섬유화약제는특이적으로활성화된간성상세포에만결합하여약제의효율성을높이고부작용은 줄일수있는장점이있다. 이들수용체와반응하는 ligand와결합된항섬유화약제는수용체를통 하여세포내로 uptake 되고있어항섬유화약제의효과적인운반(delivery) 방법으로이용되고있다. 실제로콜라젠 VI 수용체(CVIR) 와반응하는 cyclic octapeptide 와알부민이결합된약제를주사한 후약제의분포상황을장기별로살펴본연구결과활성화된간성상세포에서투여량의약 40% 이상 이관찰되었다. 활성화된간성상세포를목표로항섬유화약제를투여하는방법으로 1) IGF 수용체 를인지하는 mannose-6-phosphate 를알부민과결합시키는방법, 2) 콜라젠 VI 수용체(CVIR) 를인 - 50 -
이영석 : 만성간질환에서항섬유화치료의과거와미래 지하는 cyclic peptide 를 HAS 와결합시키는방법, 3) PDGF- 수용체를인지하는 cyclic peptide 를결 합시키는방법등이이용되고있다. 6,12,14 이러한방법을통하여간성상세포를목표로한운반방법이 개선되어한연구에서는투여량의약 70% 가간성상세포에운반되었다고보고하고있다. 항섬유화약제의복합치료 섬유화현상은간조직에서의특이한현상이아니고각종조직에서나타날수있는현상으로서항 섬유화치료에있어서조직특이성을유지하는것은매우중요한일이다. 활성화된수용체를목표로 하는항섬유화치료방법을통하여조직특이성을확보하고부작용을줄일수있게되었다. 그러나 이러한현상은항상일정하게나타나는것이아니고어느특정시기에국한되는경우도있어세심한 주의를필요로하고있다. 활성화초기에는간성상세포가 TGF-β 에예민하게반응하고있으나이 미 myofibroblast 로형질변환이끝난상태에서는 TGF-β 에대한반응이떨어지거나거의없는상 태로변해다른효과적인치료방법이강구되고있다. 최근에는서로다른기전을가진항섬유화약 제를복합하여저용량으로장기간치료하는방안이새로운치료방법으로강구되고있다. 4,14 항섬유화약제와간세포의재생촉진 간경변증은섬유화현상이진행됨에따라교원질함량이많아지고상대적으로기능을지닌간세 포의수효는줄어들어잔존간기능이감소된상태에있다. 이론적으로항섬유화약제를이용하여 간경변증을치료할때에는간세포재생촉진인자를통하여간세포의증식을시도하는방안이강구 되고있다. 세포의재생촉진으로인하여간암의발생이우려되고있으나대규모의전임상시험을 통하여항섬유화치료가간암의발생을촉진한다는근거는제시되지않고있다. 간세포성장인자 (hepatocyte growth actor, HGF) 뿐아니라( 그림 10-12) 유전자치료, 줄기세포 (stem cell) 의이용 도검토되고있으나아직은초보단계에머물러있는상황에있다. 16-51 -
2006년대한간학회 Single Topic Symposium Growth factors Cytokines Chemokines Vasoactive factors Free radicals Fibrogenesis Fibrogenesis Migration FIBROTIC LIVER ACTIVATED HSC Contraction Resolution HEPATOCYTE REGENERATION MATRIX DEGRADATION HSC APOPTOSIS Figure 10. Dual fate of activated stellate cells. Fibrogenesis ACTIVATED HSC Fibrogenesis TGF-β antagonist halofuginone Migration Small-molecule molecule tyrosine kinase inhibitors Fumigillin, glitazones Contraction Endothelin antagonists, Nitric oxide Figure 11. Inhibitors of activated stellate cells. - 52 -
이영석 : 만성간질환에서항섬유화치료의과거와미래 Fibrogenesis ACTIVATED HSC HEPATOCYTE REGENERATION HGF MATRIX DEGRADATION MMPs, upa, TIMP-1 antisense HSC APOPTOSIS Gliotoxin,, RGD peptides, sulfasalazine, death receptor ligands Figure 12. Antifibrotic agents that promote resolution of activated stellate cells. 결 론 섬유화기전에대한관심이집중되고연구방법이발달함에따라섬유화과정에대한연구에많은 발전이있었다. 정상간으로부터간경변증에이르기까지콜라젠이나세포외기질의분포상황과종 류, 섬유화과정에서간성상세포의역할, 섬유화과정에관여하는주요 cytokine 이나성장인자, 섬유의용해과정과조절인자, 간성상세포의아포토시스등여러분야에서간섬유화에대한여러 ( 분자) 생물학적특성들이밝혀졌다. 간성상세포에대한연구를통하여섬유화현상은섬유의생성 과정(fibrogenesis) 이주축을이룬 fibrosis progression-only 모델에서섬유의생성과용해과정 (fibrinolysis) 의동적인과정(dynamic process) 이주축을이룬 fibrosis reversal 모델로바뀌게 되었다. 간세포를손상시키는원인인자를제거하거나또는염증반응을완화시킴으로써섬유의생 성과정을억제하는방법이항섬유화치료의근간을이루어왔으나최근에는활성화된간성상세포 에항섬유화약제를선택적으로투입하고그세포에서약리작용을꾀하는목표지향적치료방법 (targeted antifibrotic therapy) 이시도되고있다. 개선된치료방법을통하여부작용을감소시키면 서임상효과를극대화시킬수있게되었고또한활성화된간성상세포를선택적으로사멸화 (apoptosis) 시키는치료방법이강구되고있다( 그림 13). In vitro와 in vivo 실험을통하여항섬유화 약제의많은부분이밝혀지고동물실험을통하여검증되고있으나인상치료에적용하기에는아직 - 53 -
2006년대한간학회 Single Topic Symposium 도해결되어야할문제점들이많이있다. 섬유화과정에관여하는유전인자를파악함으로써간경변 증으로진행될위험도가높은환자를선별치료하는방안이나비관혈적방법을통하여항섬유화치 료효과를판정하는방법의개발이요구되고있다. 항섬유화치료뿐아니라간세포의재생촉진이요 구되는간경변증환자에서줄기세포를이용한치료나유전자치료의역할이기대되고있다. PROGRESSION FIBROGENESIS RESOLUTION QUIESCENT HSC ACTIVATED HSC APOPTOTIC HSC HEPATOCYTE KUPFFER CELL INFLAMMATORY CELL Number HSC TIMPs Collagen Collagenase Factors favoring Survival: Cytokines/soluble factors Matrix Number HSC TIMPs Collagen Collagenase Factors favoring apoptosis: Death receptor activation Withdrawal of survival factors: Soluble factors Matrix degradation Figure 13. Factors favoring survival and factors favoring apoptosis of activated hepatic stellate cells. 참고문헌 1. Bissel DM, Maheer JJ. Hepatic fibrosis and cirrhosis. In: Zakim D, Boyer TD, ed Hepatology: A textbook of liver disease. Philadelphia: WB Saunders, 1998:506-525. 2. Li D, Friedman SL. Liver fibrogenesis and the role of hepatic stellate cells: new insights and prospects for therapy. J Gastroenterol Hepatol 1999;14:618-633. 3. Holstege A. Kollinger M, Scholmerich J. The role of fibrogenesis in the pathogenesis of portal hypertension. In: Holstege A, Hahn EG, Scholmerich J ed. Portal hypertension. Netherland: Kluwer Academic Publishers, 1955:33-50. 4. Schuppan D, Porov Y. Hepatic fibrosis: From bench to bedside. J Gastroenterol Hepatol 2002;17(suppi): 300-305. 5. Friedman SL. Molecular regulation of hepatic fibrosis, an integrated cellular response to tissue injury. J Biol Chem 2000;275:2247-2250. - 54 -
이영석 : 만성간질환에서항섬유화치료의과거와미래 6. Bataller R and Brenner DA. Liver fibrosis. J Clin Invest 2005;115:209-218. 7. Gressner AM, Meyer D. The role of proteoglycans in liver fibrogenesis. In: Gressner AM, Ramadori G. ed. Molecular and cell biology of liver fibrogenesis. Netherland: Kluwer Academic Publishers, 1992:115-136. 8. Breitkopf K, Haas S, Wiercinska E, Singer MV, Dooley S. Anti-TGF-beta strategies for the treatment of chronic liver disease. Alcohol Clin Exp Res 2005;29:121S-131S. 9. Rockey DC. Antifibrotic therapy in chronic liver disease. Clin Gastroenterol Hepatol 2005;3:95-107. 10. Tangkijvanich P, Yee HF Jr. Cirrhosis--can we reverse hepatic fibrosis? Eur J Surg Suppl 2002;587:100-112. 11. Friedman SL, Bansal MB. Reversal of hepatic fibrosis---fact or fantasy? Hepatology 2006;43(suppl):82-88. 12. Friedman SL, Maher JJ, Bissell DM. Mechanism and therapy of hepatic fibrosis: report of the AASLD single topic basic research conference. Hepatology 2000;32:1403-1408. 13. Albanis E, Friedman SL. Antifibrotic agents for liver diseases. Am J Transplant 2006,6:12-19. 14. Fallowfield JA, Iredale JP. Targeted treatments for cirrhosis. Expert Opin Ther Targets 2004,8:423-435. 15. Pinzani M, Rombouts K. Liver fibrosis: from the bench to clinical targets. Dig Liver Dis 2004,36:231-242. 16. Fowell AJ, Iredale JP. Emerging therapies for liver fibrosis. Dig Dis 2006,24:174-183. 17. Dooley S, Hamzavi J, Breitkopf K, Wiercinska E, Said HM, Lorenzen J, et al. Smad7 prevents activation of hepatic stellate cells and liver fibrosis in rats. Gastroenterology 2003;125:178-191. 18. Dooley S. Delvoux B, Streckert M, Bonzel L, Stopa M, ten Dijke P, Gressner AM. Transforming growth factor beta signal transduction in hepatic stellate cells via Smad2/3 phosphorylation, a pathway that is abrogated during in vitro progression to myofibroblasts. TGFbeta signal transduction during transdifferentiation of hepatic stellate cells. FEBS Lett 2001;502:4-10. 19. Liu X, Wang W, Hu H, Tang N, Zhang C, Liang W, Wang M. Smad3 specific inhibitor, naringenin, decreases the expression of extracellular matrix induced by TGF-beta1 in cultured rat hepatic stellate cells. Pharm Res 2006;23:82-89. 20. Wang YJ, Wang SS, Bickel M, Guenzler V, Gerl M, Bissell DM. Two novel antifibrotics, HOE 077 and Safironil, modulate stellate cell activation in rat liver injury; differential effects in males and females. Am J Pathol 1998;152:279-287. - 55 -